What is this the earth for?

[Rawhide]

I'm working on fixing a missfire under load and a slightly high idle problem.

I was planning on changing the coilpacks and HT leads today but after removing the intake system and airboxes I've run out of time and sunlight. However I've discovered a few issues.

Firstly what is the main earth cable that runs to the negative battery lead for? I found it disconnected in the car. The car has recently been serviced but I think this was my fault due to fitting an anderson connecter to the battery under torchlight recently. I must have forgotten to refit it.



What would be the symptoms of a missing earth? I was wondering if this could cause poor running under load?

Secondly my drivers side airbox I've noticed has about a six inch gap where the mastic is not holding in the 'trumpet's to the main housing. This would I expect cause air to get directly in bypassing the airbox and filter.

I wasn't expecting to find the coil packs so inaccessible. Does anyone have a guide on how to remove the fuel rail to gain access at all or it is just remove everthing I can see and then re-assemble.

Many thanks

Edited by Rawhide on Sunday 22 January 23:28

[pmessling]

no need to remove the fuel rail. once all the intake hoses are off and the HT leads there is enough room to get to the coil packs from round the back. thats how i done it when i changed mine.

[mikesr]

Is the other end of that earth cable bolted to the chassis behind the front wheel?

If it is then its probably the engine earth strap that bolts to the block.

[Rawhide]

pmessling said:

no need to remove the fuel rail. once all the intake hoses are off and the HT leads there is enough room to get to the coil packs from round the back. thats how i done it when i changed mine.

Thanks for that. I've lost a lot of skin but managed to get it done. It's a lot easier in the daytime

[ridds]

I'd put that ground back onto the stud on the chassis down in the nearside wheel arch where it is supposed to be before you go chasing anything else.

[Rawhide]

ridds said:

I'd put that ground back onto the stud on the chassis down in the nearside wheel arch where it is supposed to be before you go chasing anything else.

Hi Ridds, I'm certainly am not but are you sure? The lead in question is chased alongside the negative battery terminal wire. It's shaped and bent like it is intended to be joined to the battery terminal. It's the exact same length as well.

I'm now very keen to be sure as I've tried leaving it loose and connecting it to the negative terminal. The car won't start

I've now carefully swapped out both coilpacks (properly connected)and attached all HT leads as per the below picture. The leads are all well seated on the coilpacks and snapped on fairly lightly to the sparkplug (suprisingly easily). I've also completely repaired the airbox.



This is a 4.2 but I can't imagine it's different from a 4.5

I was so confident of my work I even re-attached all the intake hoses before trying to start the car.

I had a quick look if there was somewhere obvious where the lead could connect to the chassis which was hard with the airbox attached but I think it's too short.

I've now left it on optimate again as it was backfiring and popping as it was turning over. I didn't want to wake the neighbours or my 18 month old son so will have to try and work on it tomorow.

The car would turnover ok but would pop and die when I gave it a bit of gas so I assume it's getting fuel. I can hear the pump priming and it smells of petrol.

Edited by Rawhide on Sunday 22 January 23:23

[ridds]

You need to chase that wire then. It'll either disappear into the loom or back into the bulkhead I'd it's not a ground. If it is the battery to chassis ground then you'll find the post on the chassis near the nearside suspension mount.

Also check you have the correct plug lead wiring diagram as there are 2. You're either firing at the wrong time, hence the pops, and flooded hence the pops, or both.

[pmessling]

You could try belling the lead out to see if it's connected using a multimeter. Or voltage testing to see if you have voltage on it.

Disconnect your battery and bell the lead out to both positive and negative (negative being a good non painted part of the chassis or engine) and see what happens or where it goes. Then connect the battery.

Having another return (negative) shouldn't do any harm in any circuit although given its a TVR best side on caution

But test it then trace it.

[mikesr]

Is the other end of the cable bolted to the chassis rail where the lead from the battery is fastened?
If it is then its likely the engine earth strap.

If it disappears into the transmission tunnel then it likely goes to the earth point under the dash and the loose end should be bolted to the chassis rail with the other earths.

[Rawhide]

ridds said:

Also check you have the correct plug lead wiring diagram as there are 2. You're either firing at the wrong time, hence the pops, and flooded hence the pops, or both.

Of course there are two lead layouts.. Great! I'll strip it all out this afternoon and try and take a look.

I did a quick check of the old leads before removing them out and saw that a couple were connected in the same layout. I only did this for peace of mind that the diagram was correct and didn't check all of them.

Anyone have an idea where I can find the correct diagram? The car is a '00 4.5

Edited by Rawhide on Monday 23 January 08:55

[pmessling]

The diagram that you have used the one that's posted in the thread is the one I use for my 04 4.5 and runs perfectly.

[Rawhide]

As an update I'm working from home today so managed to remove all the intake from the rear four cylinder to get access. I found a fault. I had swapped the leads for cylinders 5 and 7.

I swapped these back and started it up with the hoses re-attached. I managed to get it very reluctantly started but it seemed like it was running on only one bank. It sounded like a four cylinder and the revs didn't want to rev. I was also getting some backfires.

I then removed all the hoses again to check the connections to the coilpacks. All HT leads are nicely seated. The coil packs are connected correctly as 'odd' and 'even'. The 'odd' coil pack the connector seems seated ok but it does pull off fairly easily. The even one is tight.

I didn't easily see which exhaust was running when the car was running.

I've left the car partially assembled whilst I have a bit of a sulk. The cylinders are probably flooded and the battery is back on the CTEK charger.

Any ideas guys?

I've re-attached the earth to the battery. I'm 90% sure that is where it belongs from the way it's laid out and bent.

[Rawhide]

I think I've had a eureka moment.

Looking at the picture I notice that the coilpacks are not in the same direction. One has the plug pointing at the odd bank and one at the even bank.



I can't remember how they were when I removed them from the car.

My coilpacks both have the plug closer to the even (passenger side) bank. I am hoping that the problem.

Would I be able to just flip the HT leads around or should I swap the coil pack around?

My time is precious and my patience thin. Could someone with more knowledge help me out before I get my hands dirty again?

Edited by Rawhide on Monday 23 January 15:47

[Rawhide]

Problem now sorted. I've 'reversed' the HT leads on the rear coil pack and the car is now purring.

Thanks all. I feel a bit stupid now!